1. Field of the Invention
The present invention relates to electrical contact devices such as multi-phase contactors. More particularly, the invention relates to a movable contact arrangement for a contactor, in the form of a modular arrangement which provides ease of assembly and replacement, as well as excellent electrical performance and isolation capabilities.
2. Description of the Related Art
A large number of electrical contact devices have been proposed and are currently in use. In one type of device, commonly referred to as a contactor, a movable conductive assembly is provided between a pair of stationary contacts. The movable assembly includes movable contacts which span the stationary contacts when the device is closed. The movable contacts may be actuated by an electromagnetic actuating assembly which, when energized, causes the movable contacts to complete a current carrying path between the stationary contacts, or to open such a path, depending upon whether the device is installed in a normally-open and normally-closed configuration.
Movable contact structures are designed to provide for rapid opening and closing of the electrical path between the stationary contact structures, as well as to endure a number of opening and closing cycles during the useful life of the device. Movable contacts have been designed, therefore, to provide various schemes for making and breaking the electrical path within a contactor to minimize arcing and other phenomena which can damage the structures. In one such arrangement, arc contacts are closed before separate shunt contacts during making of the contactor, and are opened after the shunt contacts upon breaking. In either case, the devices are typically designed so as to promote migration of arcs away from contact pads on the stationary and movable contacts towards splitter plates and similar structures which serve to cool and extinguish the arcs. Moreover, in multi-phase devices, dividers, partitions, or similar arrangements are typically provided between movable and stationary contact sections for each phase, to avoid phase-to-phase short circuits during opening and closing.
Despite improvements in arc handling and isolation in contactors of the type described above, persistent difficulties still exist. For example, in many contactors movable contact structures are provided in a single modular unit, typically including a carrier assembly for linking the movable contacts to an actuating assembly. If, over time, the movable contacts are damaged due to arcing, pitting, and similar phenomena, the entire movable contact assembly must be replaced. Depending upon the size of the contactor, this assembly can be quite large and expensive. Moreover, depending upon the manner in which the movable contact assembly is supported and connected with associated components within the device, extensive dismantling of the contactor may be required for the replacement of the assembly.
In addition to the foregoing drawbacks, movable contact assemblies have often been structured in less than optimal arrangements from a mechanical standpoint. For example, conductive spanning elements in movable contact assemblies are typically resiliently biased toward a contact position in the assembly such that some flexibility of movement will be possible when the movable contact is urged against stationary contacts. This arrangement typically takes the form of a tensioned member surrounding at least a portion of the movable conductive spanner, and springs extending between the spanner and the tension member. The resulting structure requires a number of independent parts to be manufactured and assembled in the stationary contact, adding to the cost and complexity of the structure. In addition, biasing components, including springs and tension members may be difficult to isolate physically and electrically from the movable conductive spanner. Thermal, electrical, and magnetic cycling of the contactor can result in mechanical damage to the biasing elements, particularly to the biasing springs. Such damage can take the form of burning, pitting, depositing of metal particles, or alteration of the material properties of the spring, leading to a reduction in its spring force over time, and consequent degradation in performance.
There is a need, therefore, an improved movable contact structure for electrical contact devices. In particular, there is a need for a movable contact structure which addresses the drawbacks of existing structures, providing both electrical and mechanical isolation of conductive elements within the movable contact structure from mechanical elements which may be subject to damage, as well as a structure which is both straight forward to assemble and replace. There is also a need for improved movable contact arrangements which are straightforward to assemble, install and replace as needed through the life of the device.